Electric vehicles (EVs) have been actively studied because they are the most promising solution to pollution and energy problems.
Electric vehicles (EVs) are mainly powered by an AC or DC motor using power of a battery. The electric vehicles are broadly classified into battery powered electric vehicles and hybrid electric vehicles. In the battery powered electric vehicles, a motor is driven using power of a battery, and the battery is recharged after stored power is consumed. In hybrid electric vehicles, a battery is charged with electricity generated via engine driving, and an electric motor is driven using the electricity to realize vehicle movement.
The hybrid electric vehicles may further be classified into serial and parallel types. In the case of serial hybrid electric vehicles, mechanical energy output from an engine is changed into electric energy via a generator, and the electric energy is fed to a battery or motor. Thus, the serial hybrid electric vehicles are always driven by a motor similar to conventional electric vehicles, but an engine and generator are added for the purpose of increasing range. Parallel hybrid electric vehicles may be driven using two power sources, i.e. a battery and an engine (gasoline or diesel). Also, the parallel hybrid electric vehicles may be driven using both the engine and the motor according to traveling conditions.
With recent gradual development of motor/control technologies, small high-output and high-efficiency systems have been developed. Owing to replacing a DC motor by an AC motor, electric vehicles have accomplished considerably enhanced output and power performance (acceleration performance and maximum speed) comparable to those of gasoline vehicles. As a result of promoting a higher output and higher revolutions per minute, a motor has achieved reduction in weight and size, and consequently reduction in the weight and size of a vehicle provided with the motor.
Energy supplied from a high-voltage battery of the electric vehicle is PWM-switched by the converter such that a battery voltage of several hundreds of V is converted into a voltage of about 12V and thus the resultant voltage is supplied to an auxiliary battery and overall load.
An output voltage of the converter is slightly higher than a normal voltage of the auxiliary battery, such that the converter can charge the auxiliary battery and at the same time can provide energy to necessary loads. Therefore, provided that the load is increased in size, not only capacity of the converter but also the size of the converter must be increased.
As a result, although the size of load is increased, rated capacity of the converter needs to remain constant.